This application claims the benefit and priority of Japanese Patent Application No. 2001-005478, filed Jan. 12, 2001, and Japanese Patent Application No. 2001-111685, filed Apr. 10, 2001, the contents of which are incorporated herein by reference.
The present invention relates to hydraulic units for use in electric power tools such as torque wrenches for generating pulsating instantaneous torque by means of hydraulic pressure.
FIG. 6 shows a conventional hydraulic unit 50. The hydraulic unit includes a cylindrical case 51 which integrally accommodates a liner 52 coupled to the output shaft of a tool motor for receiving torque therefrom. The hydraulic unit 50 further includes front and rear caps (not shown) as closing elements that plug the axial front and rear ends of the case 51, thus forming a fluid chamber 53 therein. The front and rear caps also rotatably support a spindle 54 within the fluid chamber 53. Furthermore, inserted radially in the spindle 54 is a pair of blades 55 that are biased generally outwardly in mutually opposing directions by a coil spring 62 so that the blades can be retracted into the spindle when inward pressure exceeding the biasing force of the coil spring is applied to the top surfaces of the blades 55. The spindle 54 additionally includes a pair of ribs 56 which protrudes therefrom at diametrically opposite positions and which are 90 degrees phase-shifted from the blades 55. Formed at the axial front and rear ends of the liner 52 are two generally oblong guide holes 57 along which the top surfaces of the blades 55 slide. Two axially extending first sealing bodies 58 are disposed between the guide holes 57, with each sealing body 58 provided with a first sealing surface 59 which is flush with and conforms to the interior surface of the guide hole 57. Additionally, two axially extending second sealing bodies 60 are disposed between the guide holes 57, with each sealing body 60 provided with a second sealing surface 61 which also conforms to the interior surface of the guide hole 57. The first sealing bodies 58 are 90 degrees phase-shifted from the second sealing bodies 60. As shown in FIG. 6A, in the operation of the electric power tool, as the liner 52 rotates in the direction indicated in the arrow, the blades 55 rotate relative to the case 51 along the interior surfaces of the guide holes 57. When the blades 55 reach the first sealing surfaces 59 and the ribs 56 reach the second sealing surfaces 61, the fluid chamber 53 are divided into four partitions, creating alternate high and low pressure chambers. This differential pressure in the fluid chamber causes generation of impact torque (generation of a hydraulic impulse) to the spindle 54. One example of such an hydraulic unit is disclosed in Japanese Published Examined Utility Model Application No. 6-27341.
In the foregoing hydraulic unit 50, upon generation of a hydraulic impulse, the liner 52 continues its rotation, thus removing the blades 55 and the ribs 56 from the first and second sealing surfaces 59 and 61, respectively. As the seal within the fluid chamber 53 is opened at this moment, no hydraulic impulse is generated, such that the liner 52 alone rotates (FIG. 6B). As the liner 52 continues its rotation, the blades 55 slide along the interior surfaces of the guide holes 57, approaching the second sealing surfaces 61. As this gradually pushes the blades 55 into the spindle 54, the basing force of the coil spring 62 against the blades 55 increases (FIG. 6C) until it peaks when the blades reaches the second sealing surfaces 61 (FIG. 6D). Accordingly, the blades"" pressure on the interior surfaces of the guide holes 57 acts as rotational resistance to the spindle 54, thus impeding its rotation. In addition, as illustrated, the cross section of the guide holes 57 is a combination of three circles such that the guide holes 57 have low axial ridges on both sides of each second sealing surface 61, where the intermediate circle intersects the two side circles. Thus, as shown in FIG. 6D, when the blades 55 ride over the intersection points P, additional resistance to rotation of the blades 55 is created.
FIG. 8 is a graph showing a pattern of torque production in the conventional hydraulic unit 50. Peaks xe2x80x9caxe2x80x9d indicate intended torque produced by hydraulic impulses, whereas lower torque peaks xe2x80x9cbxe2x80x9d are produced between these hydraulic impulses by the above-described rotational resistance. Such useless low torque disadvantageously decreases the intended torque produced by hydraulic impulses.
FIG. 7 shows another conventional hydraulic unit 50xe2x80x2 similar to the foregoing conventional hydraulic unit 30. FIGS. 7A-L are similar to FIGS. 6A-D, but they show the movement of the blades 55xe2x80x2 with respect to the case 51xe2x80x2 in a more detailed sequence, with each figure depicting unit""s parts or elements in the position 10 degrees further rotated from the position in the immediately preceding figure. Additionally, identical or similar reference numerals or characters denote identical or similar parts or elements of those in FIG. 6 throughout the several views. Therefore, description of such elements is omitted.
As shown in FIGS. 7A-C, when the blades 55xe2x80x2 and the ribs 56xe2x80x2 reach the first and second sealing bodies 58xe2x80x2 and 60xe2x80x2, respectively, with the counterclockwise rotation of the case 51xe2x80x2 and the liner 52xe2x80x2, the fluid chamber 53xe2x80x2 is divided into four partitions or sub-chambers, thus producing impact torque (hydraulic impulse), as in the foregoing unit 30. Referring to FIGS. 7D-L, following the production of impact torque, as the liner 52xe2x80x2 continues to rotate, the blades 55xe2x80x2 are gradually retracted into the spindle 54xe2x80x2 against the biasing force of the coil spring and eventually slide across the second sealing bodies 60xe2x80x2 over the ridges on the inner surfaces of the guide holes 57xe2x80x2. Compared to FIG. 6, FIGS. 7D-L illustrate in greater detail the increased resistance to the rotation of the spindle 54xe2x80x2 due to the cross section of the guide holes 57xe2x80x2 being a combination of three circles.
Moreover, as the cross section of the guide holes has a complex shape due to the combination of three intersecting circles, the interior surfaces of the guide holes 57xe2x80x2 requires high-precision polishing, thus increasing the number of manufacturing steps and resulting in higher cost.
In the foregoing hydraulic unit 60xe2x80x2, the cross section of the guide holes 57xe2x80x2 of the liner 52xe2x80x2 is a combination of three circles, and the first and second sealing bodies 58xe2x80x2 are required, thus making the entire structure of the liner complex.
In view of the above-identified problems, the present invention provides a hydraulic unit wherein the rotational resistance to the spindle can be effectively reduced except upon generation of hydraulic impulses, thus augmenting the torque produced by such hydraulic impulses.
The present invention also provides a hydraulic unit which has a simplified construction and thus a greater cost advantage over conventional hydraulic units.
In accordance with one embodiment of the present invention a hydraulic unit is provided including a generally cylindrical case containing working fluid, with the case including an interior surface, front and rear closing elements at two axial ends thereof, and at least one first blade-sealing surface and at least one second rib-sealing surface. The hydraulic unit further includes a spindle which is inserted into the case and includes front and rear ends rotatably supported by the front and rear closing elements, respectively, with the spindle further including at regular intervals at least one blade and at least one rib for circumferentially partitioning an interior of the case into a plurality of smaller fluid chambers whereby relative rotation between the case and the spindle causes top surfaces of the at least one blade and the at least one rib to slide along the interior surface of the case so as to create differential pressure among the small fluid chambers when the top surfaces of the blade and the rib reach the first and second sealing surfaces, respectively, thus generating instantaneous torque to the spindle. Additionally included in the hydraulic unit are a pair of pins provided on axial front and rear ends of each blade and cam recesses provided in opposing inner surfaces of the closing elements of the case. In this hydraulic unit, during rotation of the case, the cam recesses guide the pins and prevent the top surfaces of the blades from sliding on the second rib-sealing surfaces. This arrangement completely eliminates the rotational resistance created by the top surfaces of the blades riding over the sealing surfaces associated with the ribs, thereby maximizing the torque resulting from intended hydraulic impulses. It should be noted that as used herein, the term xe2x80x9coblongxe2x80x9d is intended to include xe2x80x9cellipticalxe2x80x9d as well as xe2x80x9celongated circle.xe2x80x9d
In accordance with one aspect of the present invention, the spindle includes first and second blades, the case includes two second blade-sealing surface, the first blade is provided with two first pins, the second blade is provided with two second pins shorter than the first pins, and each closing element includes in its inner surface a first oblong cam recess for guiding one of the first pins and a second oblong cam recess shallower than the first cam recess for guiding one of the second pins. In this aspect, each first cam recess shares a common longitudinal end portion with the second cam recess and has a shorter longitudinal axis than the second cam recess such that the first blade is prevented from coming into slidable abutment with one of the second blade-sealing surfaces by the first recess guiding the first pins. This ensures generation of one hydraulic impulse per rotation of the case, which further augments the unit""s output torque each time torque is generated.
In accordance with another aspect of the present invention, while the first recesses prevent the first blade from coming into abutment with one of the blade-sealing surfaces, the second recesses cooperate with the second pins to permit the second blade to protrude into abutment with the other blade-sealing surface.
In accordance with yet another aspect of the present invention, the first and second blade are located diametrically opposite about the axis of the spindle, two ribs are positioned diametrically opposite about the axis of the spindle and 90 degrees phase-shifted from the blades, two rib-sealing surfaces are positioned diametrically opposite about the center axis of the interior surface of the case, the longitudinal axes of the first and second cam recesses are oriented orthogonal to a diameter of the case passing through the rib-sealing surfaces, and the widthwise axes of the second cam recesses pass through the axis of the spindle and are oriented orthogonal to the longitudinal axes of the first and second cam recesses, and the center of the second cam recess is located at the axis of the spindle. In this arrangement, when the case is at a first rotational position, the rib-sealing surfaces oppose the ribs and each second pin is located on the longitudinal axis of the associated second cam recess in the longitudinal end portion of the second recess not shared with the first recess while each first pin is located on the longitudinal axis of the first and second recess in the longitudinal end portion shared by the first and second recesses so as to allow the blades to be biased into abutment with the interior surface, thus producing instantaneous torque, and at a second rotational position of the case, rotated a further 180 degrees from the first rotational position, each second pin is located on the common longitudinal axes of the first and second cam recesses in the longitudinal end portion shared by the recesses and each first pin is located on the longitudinal axes of the first cam recess in the first cam""s longitudinal end portion not shared with the second cam recess, thus preventing the first blade from coming into abutment with the interior surface.
In accordance with still another aspect of the present invention, the widthwise axes of the first and second cam recesses are selected so as to have a common and sufficiently short length to cause the blades to be retracted into the spindle when the case is at a third rotational position, rotated a further 90 degrees from the first position, where the first and second pins are located approximately on the widthwise axes of the second cam recesses, with the blades passing by the rib-sealing surfaces.
According to one feature of the present invention, each cam recess includes a pair of opposing semicircular walls and a pair of parallel liner walls connecting the semicircular walls, thus forming a continuous loop surface extending parallel with the axis of the spindle, and additionally, each of the aforementioned longitudinal end portions shared by the first cam recess and the associated second cam recess includes one semicircular wall and at least part of each liner wall.
According to another feature of the present invention, following the retraction of the blades into the spindle, when the case is at the third rotational position, the case returns to the first rotational position upon rotating a further 270 degrees, such that instantaneous torque is produced to the spindle once for each complete rotation of the case.
According to still another feature of the present invention, the hydraulic unit further includes a pair of coil springs disposed between the blades within the spindle for biasing the blades in outwardly radial directions, and the first and second pins are inserted in the respective first and second recesses. Additionally, the length of each second pin in the recesses is shorter than the portion shared by the first and second recesses and the length of each first pin in the cam recesses is shorter than the depth of the first cam recess and greater than the depth of the portion shared by the first and the second cam recesses.
According to yet another feature of the present invention, the case further includes a liner which is integrally rotatable with the case and defines the interior surface of the case, a transversal cross section of the interior surface of the case has an approximately oblong shape of a combination of three circles whose centers are located on a common straight line such that two pairs of axial ridges are symmetrically formed about the common line where the intermediate circle intersects the two side circles. The case further includes two rib-sealing surfaces, each of which is located at an intermediate position between the two ridges on either side of the common line and flush with the interior surface of the case, and the spindle further includes a large diameter section between the rear and front ends thereof, the large diameter section having a transversal cross section complementary to and snugly fitting in the intermediate circle, and the large diameter section includes two pairs of mutually parallel axial chamfers formed in an outer peripheral surface thereof to define one of the ribs between each pair such that when the rib-sealing surfaces of the case are displaced by rotation from the ribs, the chamfers undo the sealing provided by the rib-sealing surfaces opposing the ribs. In addition, the rib-sealing surfaces oppose the outer peripheral surface of the large diameter section except when the rib-sealing surfaces oppose the chamfers, whereas the case further including thereon two blade-sealing surfaces which are 90 degree phase-shifted from the rib-sealing surfaces.
In accordance with one embodiment, a hydraulic unit includes: a generally cylindrical case containing working fluid, with the case including an interior surface and front and rear closing elements at two axial ends thereof; a spindle which is inserted into the case and includes front and rear ends coaxially and rotatably supported by the front and rear closing elements, respectively, the spindle further including at least one axially extending sealing surface and at least one blade which is biased radially into abutment with the interior surface of the case for circumferentially partitioning a fluid chamber defined between the case and the spindle; at least one axially extending sealing body protruding from the interior surface of the case and opposing the at least one sealing surface of the spindle for sealing the fluid chamber when the case is at a predetermined rotational position; a pair of pins provided on axial front and rear ends of each blade; and cam recesses provided in opposing inner surfaces of the closing elements for guiding the pins during rotation of the case and retracting the blades into the spindle when the at least one sealing body passes by the at least one blade, in which while relative rotation between the case and the spindle causes a top surface of the at least one blade to slidably abut the interior surface of the case, the at least one sealing body opposes the at least one sealing surface so as to divide the fluid chamber into smaller chambers, thus creating differential pressure among the smaller chambers, thus producing instantaneous torque to the spindle. Furthermore, the interior surface of the case has a circular shape coaxial with an axis of the spindle. Since the interior surface of the case has a simple circular cross-section coaxial with the spindle, the case functions as a liner in conventional arrangements, thus reducing the number of components in the foregoing hydraulic unit. In addition, as the interior surface of the case need only be machined to a simple circular hole, eliminating the need for high-precision polishing, as is required for complexly shaped interior surfaces of conventional units, and significantly lowering the cost and number of steps required in manufacturing the hydraulic unit.
In accordance with one aspect of the present invention, the spindle includes first and second blades and the case includes two sealing bodies, the first blade is provided with two first pins, and the second blade is provided with two second pins longer than the first pins. Moreover, each closing element includes in its inner surface a first oblong cam recess for guiding one of the first pins and a second oblong cam recess deeper than the first cam recess for guiding one of the second pins. Each second cam recess shares a common longitudinal end portion with the first cam recess and has a shorter longitudinal axis than the first cam recess such that, following the retraction of the blades into the spindle, the second recesses prevent the second blade from coming into abutment with the interior surface of the case until the case further rotates a predetermined angle while the first recesses cooperate with the first pins to permit the first blade to protrude into abutment with the interior surface of the case.
In accordance with another aspect of the present invention, the first and second blade are located diametrically opposite about the axis of the spindle, two sealing surfaces are positioned diametrically opposite about the axis of the spindle and 90 degrees phase-shifted from the blades, and two sealing bodies are positioned diametrically opposite about the axis of the interior surface of the case. Additionally, the longitudinal axes of the first and second cam recesses are oriented orthogonal to a diameter of the case passing through the sealing bodies, the widthwise axes of the first cam recesses pass through the axis of the spindle and are oriented orthogonal to the longitudinal axes of the first and second cam recesses, and the center of the first cam recess is located at the axis of the spindle. In this arrangement, when the case is at a first rotational position, the sealing bodies oppose the sealing surfaces and each first pin is located on the longitudinal axis of the associated first cam recess in the longitudinal end portion of the first recess not shared with the second recess while each second pin is located on the longitudinal axis of the first and second recesses in the longitudinal end portion shared by the first and second recesses so as to allow the blades to be biased into abutment with the interior surface of the case, thus producing instantaneous torque. At a second rotational position of the case, rotated a further 180 degrees from the first rotational position, each first pin is located on the common longitudinal axes of the first and second cam recesses in the longitudinal end portion shared by the recesses and the second pin is located on the longitudinal axis of the second cam recess in the second cam""s longitudinal end portion not shared with the first cam recess, thus preventing the second blade from coming into abutment with the interior surface.
In accordance with yet another aspect of the present invention, the widthwise axes of the first and second cam recesses are selected so as to have a common and sufficiently short length to cause the blades to be retracted into the spindle when the case is at a third rotational position, rotated a further 90 degrees from the first position, where the first and second pins are located approximately on the widthwise axes of the first cam recesses, with the blades passing by the sealing bodies.
In accordance with still another aspect of the present invention, the spindle includes an outer peripheral surface having a circular cross-section coaxial with the interior surface of the case. The spindle further includes two pairs of mutually parallel axial chamfers formed therein to define one of the sealing surfaces between each pair such that when the sealing bodies of the case are displaced by rotation from the sealing surfaces, the chamfers undo the sealing provided by the sealing bodies opposing the sealing surfaces.
In accordance with one aspect of the present invention, the sealing bodies oppose the outer peripheral surface of the spindle except when the sealing bodies oppose the chamfers.
In accordance with another aspect of the present invention, each cam recess includes a pair of opposing semicircular walls and a pair of parallel liner walls connecting the semicircular walls, thus forming a continuous loop surface extending parallel with the axis of the spindle. In addition, each of the aforementioned longitudinal end portions shared by each first cam recess and the associated second cam recess includes one semicircular wall and at least part of each liner wall.
In accordance with one aspect of the present invention, the hydraulic unit further includes a pair of coil springs disposed between the blades within the spindle for biasing the blades in outwardly radial directions.
In accordance with another aspect of the present invention, following the retraction of the blades into the spindle when the case is at the third rotational position, the case returns to the first rotational position upon rotating 270 degrees further, such that instantaneous torque is produced to the spindle once for each complete rotation of the case.
In accordance with still another aspect of the present invention, the first and second pins are inserted in the respective first and second recesses. Moreover, the length of each first pin in the recesses is shorter than the depth of the portion shared by the first and second recesses, whereas the length of each second pin in the cam recesses is shorter than the depth of the second cam recess and greater than the depth of the portion shared by the first and the second cam recesses.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and descriptions which follow.